1. Field of the Invention
The present invention generally relates to a bicycle sprocket. More specifically, the present invention relates to a bicycle sprocket configured to be mounted to a rotational drive unit such as a crank of a bicycle via a synthetic resin fastening part and to have a bicycle (drive-purpose) chain wrapped around the outside circumference of a sprocket ring part thereof.
2. Background Information
A bicycle is generally provided with a drive unit or drive train having front and rear sprockets and a chain wrapped around the sprockets. The front sprocket(s) is provided on the gear crank of the bicycle and the rear sprocket(s) is provided on the free hub of the bicycle. This type of bicycle sprocket is made of such materials as the aluminum having the designation A2014P under the standard JIS H4000 (category) or the iron having the designation SPCC under the standard JIS G3141 (category). When a plurality of sprockets are mounted to the gear crank and free hub in order to provide multiple gears, aluminum is used as the material in order to reduce the weight.
There are also known bicycle sprocket designs that reduce the weight even further by having a sprocket ring part that is made of aluminum and has the sprocket teeth formed thereon and a fastening part that is made of a carbon fiber material, attached to the inner circumference of the sprocket ring part, and fastened to the gear crank (see German Utility Model Publication No. 20218755). In the case of this sprocket, the fastening part and an inner circumferential portion of the sprocket ring part are fastened together by installing crimp pins in semicircular holes provided in the sprocket ring part and the fastening part. Since the sprocket is made using two separate members, a gap is provided between the sprocket ring part and the fastening part in order to prevent deformation caused by the effects of weather. In addition, mounting holes with steps are formed in the fastening part of the gear crank. In the sprocket constructed in this manner, generally, a bolt (an example of fixed member) is passed through the mounting hole, and the sprocket is fixed to a spider arm of the gear crank via the bolt and the fastening part.
In the conventional bicycle sprocket just described, age deterioration of synthetic resin fastening part can occur at certain areas resulting in a potential loss of attachment forces. In addition, if the fastening bolts are tightened with too much torque, the synthetic resin fastening part can become deformed, and as the result, there is a possibility for reduced attachment forces. Any reduction in attachment forces can result in play or looseness, adversely affecting operation of the sprocket, shifting of the chain and/or potentially decreasing efficiency of power transfer from the rider to the chain.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved bicycle sprocket. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.